In communications systems, there may be a challenge to obtain good performance and capacity for a given communications protocol, its parameters and the physical environment in which the communications system is deployed.
For example, basic requirement for any cellular communications system is the possibility for a wireless device to initially request a connection setup, commonly referred to as random access. In Long Term Evolution (LTE) communications systems, the random access procedure comes in two forms, allowing the random access to be either contention-based or contention-free. The contention-based procedure comprises four-steps; a first step of preamble transmission, a second step of random access response, a third step of protocol Layer 2/Layer 3 message transmission, and a fourth step of contention resolution message exchange.
In LTE, the preamble sequences in the first step are generated from cyclic shifts of a root Zadoff-Chu (ZC) sequence. Sequences obtained from cyclic shifts of different ZC sequences are not orthogonal. Therefore, orthogonal sequences obtained by cyclically shifting a single root sequence should be favored over non-orthogonal sequences. The preamble sequence is by the wireless device sent in a time-frequency slot towards a radio access network node in the communication system.
Once detecting the preamble in the time-frequency slot, the radio access network node would in the second step send a Random Access Response (RAR) on the so-called Physical Downlink Shared CHannel (PDSCH), and addressed by an identity (ID), Random Access Radio Network Temporary Identifier (RA-RNTI), which conveys the identity of the detected preamble, a timing alignment instruction to synchronize subsequent uplink transmission from the wireless device, an initial uplink resource grant for transmission of the message in the third step, and an assignment of a temporary Cell Radio Network Temporary Identifier (C-RNTI).
In the third step, the wireless device would convey the actual random access procedure message, such as a radio resource control (RRC) connection request, tracking area update (TAU), or scheduling request.
In the fourth step, the contention resolution message would be sent by the radio access network node.
It is foreseen that emerging wireless communications systems may benefit from the use of a large number of antenna elements at the radio access node (possibly also at the wireless device), especially in conjunction with higher carrier frequencies than used in current wireless communications systems.
Hence, there is a need for an improved reception of identification signals from a wireless device.